My computer has a 1000w power supply. A new freezer, a dishwasher, a large flat screen is gonna cause that kind of increase. I ran (When I grew at the house) 2 1Ks, 2 400s, with the associated fans, dehumidifiers and A/Cs. It raised my bill about $100. Nobody batted an eye. When I moved to my shop and really ramped things up with 4 1Ks, 6 400s, T-5s and the other fans and A/Cs, it bumped my power bill by about $200. People tend to think that their power usage is being monitored and it just isn't. With a 400w light and the associated hardware, you'll have less an increase than you would if you bought a new freezer or big flat screen.